Comet C2012S1 ISON
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C2012S1 ISON A newly discovered comet has the potential to put on a dazzling celestial display late next year, when it will be so bright you may be able to see it briefly in the daytime sky. The most exciting aspect of this new comet concerns its preliminary orbit, which bears a striking resemblance to that of the "Great Comet of 1680." That comet put on a dazzling show; it was glimpsed in daylight and later, as it moved away from the sun, it threw off a brilliantly long tail that stretched up from the western twilight sky after sunset like a narrow searchlight beam for some 70 degrees of arc. (A person's clenched fist, held at arm's length, covers roughly 10 degrees of sky.) The fact that the orbits are so similar seems to suggest Comet ISON and the Great Comet of 1680 could related or perhaps even the same object.Comet ISON will be barely visible to the unaided eye when it is in the predawn night sky, positioned against the stars of Leo in October 2013. On Oct. 16 it will be passing very near both Mars and the bright star Regulus both can be used as benchmarks to sighting the comet. In November, it could be as bright as third-magnitude when it passes very close to the bright first-magnitude star Spica in Virgo. The few days surrounding the comet's closest approach to the sun on Nov. 28, 2013, are likely to be most interesting. It will whirl rapidly around the sun in a hairpin-like curve and perhaps becomes a dazzlingly bright (negative-magnitude) object.